Vibratory finishing method



Sept. 8, 1970 w.'R. CARTER VIBRATORY FINISHING METHOD Filed July 15,1968 R H mm m Ra m 0 AW 1 6 K 4 M M W/ L Y W. B

United States Patent Oifice 3,527,000 Patented Sept. 8, 1970 3,527,000VIBRATORY FINISHING METHOD William Randell Carter, Houston, Tex.,assignor to Geo Space Corporation, Houston, Tex., a corporation of TexasFiled July 15, 1968, Ser. No. 744,972 Int. Cl. B24b 1/00 US. Cl. 51-3164 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND. OF THE INVENTION Duringmotion finishing operations such as deburring, descaling or burnishing,practically millions of microscopic particles need be removed from thework piece. If these particles are not removed from the work piece orare allowed to redeposit thereon during the finishing operation, thework piece must be frequently rejected because it is neither chemicallynor physically clean.

Various finishing methods are known ranging from hand operations tosemi-automatic and fully automatic operations. In the past to achievethe highest degree of finish on relatively delicate parts, especiallymade of nonferrous or plastic materials, hand operations were almostexclusively employed. For example, in the manufacture of certaingeophysical transducers such as geophones and hydrophones, .thin-walledaluminum parts are employed which need be thoroughly deburred.

Prior to my method, it was necessary that these machined aluminum partsbe sandblasted and each individually hand buffed With a nylon rotarybrush. The buffed parts Were subsequently rinsed in one or moredetergent solutions. These hand finishing manipulations were relativelyexpensive and considerably raised the price of the products requiringsuch high finish.

Yet for other parts various techniques and machines are known which areused to perform the necessary finishing operations such as deburring.One such well-known method employs a vibratory machine having aprocessing tub. mountedon suitablevibration imparting means as on avertically mounted vibratory motor. Eccentric weights may be mounted onboth top andbottom of the motors shaft. Adjusting both the position andsize of the weights varies the impact force delivered by the vibratorymotor.

The use of such vibratory machines requires that the parts be combinedwith suitable media and chemical compounds to form a workload. Theefiiciency of the finishing method depends on the combined efiiciency ofthe employed media, compounds and finishing machine. The latter areselected on the basis of the desired finishing operation to be performedfor example, deburring, descaling, radiusing, cleaning, etc.

The finishing machines include tumbling machines, vibratory machines andothers. For best results with 'the method of this invention it ispreferred to employ vibra-, tory machines. Vibratory machines producethe greatest relative motion between the parts to be finished and thepart move within the confined area of the hole and perform internalfinishing. Similar action takes place in machined or recessed areasthroughout the part.

Various factors contributing to successful finishing operations areknown. These depend on the amount of material to be removed, the sizeand weight of the parts, and the final micro-inch finish desired.Nevertheless even by controlling these factors the vibratory machineswere found unsuitable for finishing lightweight, relatively small parts,especially parts having relatively confined recessed areas thereon. Suchparts when placed in a vibrating machine cannot withstand the roughhandling to which they become subjected during the vibrating cycle. Suchparts often collide against each other or against the center post of thevibrating machine. These collisions cause some of the parts to becomedamaged and others to receive a poor finish.

Accordingly, it is a broad object of this invention to provide a new andimproved method for use with conventional vibratory machines, whichmethod allows the mechanical processing of relatively fragile andlightweight parts in conventional vibratory machines.

FIG. 1 shows in cross-section a typical vibratory machine;

FIG. 2 is a view of the work load within the vibratory machine; and

FIG. 3 shows typical parts which can be processed by the method of thisinvention.

Referring to the figures there is shown a typical vibratory machine. Onesuch machine may be purchased from the Roto Finish Company in Kalamazoo,Mich. An electric motor 10 is directly bolted to a cylindrical centerpost 12 supporting a process tub 14. Eccentric weights 16 and 18 aremounted on the upper and lower ends of the motor shaft, respectively.Cylinder 12 is mounted on coil springs 20 to allow the tub 14 to vibratethereon. A suitable plastic lining made of Adiprene (trademark of DuPont) covers the walls of the process tub, as shown. The lining isabrasion resistant, relatively resilient and exhibits excellentresistance to oils, water, and many chemicals. Vibratory action istransmitted to the processing tub by motor 10. Means (not shown) areprovided to easily adjust the weights 16 and 18, thereby varying theimpact force of the vibratory motor and controlling the moving rate ofthe parts in the machine.

The work load 22 in tub 14 consists of abrasive media 24, chemicalcompound additives, water and parts 26 to be finished. Vibratory actiontakes place throughout the work load and all parts are processeduniformly and simultaneously. Such a vibratory machine can be operatedas a continuous automatic finishing machine or as a batch,automatic-finishing machine, as is well known in the art. .It isimportant that the proper motion be imparted to the parts. This motioncauses the work load 22 to become propelled in a spiral orbital patharound the tub with tridimensional vibration. The parts move in orbitalpaths, such as path 30. When they reach the summit 32 on path 30 theybreak away from the media 24 and fall into valley 34 between the centerpost 12 and the vibrating work load 22.

There are six principal operating parameters controlling the vibratoryfinishing operation:

(1) Media are selected by size or shape since it is not desired thatthey lodge in holes, projecting parts or recesses. Media are alsoselected on the basis of the desired finish. It is advantageously withrelatively complicated parts to combine both large and small media.

(2) The proportion of media-to-parts is selected depending on the sizeand fragility of the parts to be finished.

(3) Water is added to the medium to control the cutting speed and thefinal luster and finish of the parts. The cutting action of abrasivemedia is reduced as the amount of water is increased. It is alsorecognized that the amount of water added to the work load has an effectin controlling damage to the parts. For that reason operators usuallyadd relatively large quantities of water both to reduce the abrasiveaction of the media 24 and to act as a cushioning agent for the parts26.

(4) Chemical compounds are added to the media and the water. Severalhigh-quality compounds are commercially available and allow greatversatility in finishing procedures. These compounds can be bothabrasive and non-abrasive, depending on the final finish desired. Theyare available in both coarse and fine-grit sizes for most efficientfinishing operations.

(5) The amplitude, frequency, and speed of the vibrating tub have animportant effect on the success of the finishing operation. When theseare properly selected the work load 22 receives proper motion whichcauses the work load to move in an elliptical path for maximum relativemotion between media and parts. For fragile parts or those requiring amicro-inch finish, relatively low speeds are preferred.

(6) The processing time in the tub is an important parameter and normalyranges from about 5 minutes to 2 hours.

While vibratory machines dilfer in design, they operate in substantiallysimilar fashion. Another machine found acceptable to carry out themethod of this invention is manufactured 'by the SouthwesternEngineering Company of Los Angeles, Calif., and is sold under thetrademark of SWECO.

As previously mentioned, in spite of controlling the above and otherparameters, it was not possible, to my knowledge, to use such vibratingmachines for the finishing of relatively delicate parts 39 such as areshown in FIG. 3. These aluminum parts are machined and are characterizedby recesses such as 40, 42 and 44. When parts 39 would reach the summit32 on orbital path 30, they would fall into the valley, collide againsteach other and against the center post 12. As a result parts 39 wouldbecome damaged. Also, the relative motion between the parts and themedia would frequently cease, thereby preventing the parts fromreceiving a proper finishing action.

In accordance with my invention, a cushion or layer of gas bubbles 52 isformed especially around the center post 12. Bubbles 52 form arelatively thick foam 54. Foam 54 causes the parts 39 to fall itno thevalley 34 gently, keeps the parts properly separated, prevents them fromcolliding against each other and against the center post, and allows theparts to move in their orbital paths in a three dimensional vibration.

In one application the work load' 22 was made of 150 pounds of NortonNo. 8 silicon carbide natural, 150 pounds Norton No. 10 siliconcar-bide, 8 ounces of 3M Hom't 300 micro-cut, and 8 ounces of water. Thewater combines with the micro-cut to form a viscous layer of foam aroundthe center post to protect the parts. Since micro-cut is also anabrasive detergent, it cleans the parts as they vibrate.

While soap detergents and other abrasive chemical compounds werepreviously employed, they were usually employed with such relativelyhigh quantities of water that no substantial layer of foam was created.As a matter of fact, steps were generally taken to avoid the formationof a layer of foam.

While applicant has suggested a suitable work load, it will be apparentto those skilled in the art that other media and other compounds can becombined to achieve optimum finishing results on relatively fragile andlightweight parts. It is important however that the quantity of wateradded, or other equivalent liquid for mixing with the chemicalcompounds, be controlled to obtain a continuous and consistent viscouslayer of foam to properly cushion the parts in the vibratory load andagainst the sidewalls of the tub.

It will also be recognized that while the layer of foam was obtained bychemically combining compounds and water, other methods may be employedto produce gas bubbles to achieve similar results. The inventiontherefore is to be interpreted by the scope of the attached claims.

What I claim is:

1. The method for finishing relatively delicate articles of manufacturewhich includes the steps of:

placing said' articles in a vibrating machine,

combining said articles in said vibrating machine with at least suitableabrasive materials to form a work load,

vibrating said machine to vibrate said work load thereby causingrelative movements between said articles and said abrasive materials,and

establishing in at least a portion of the vibrating work load asubstantial cushion of air bubbles, said cushion acting to prevent saidarticles from damaging collisions between themselves and against theinner walls of said machine thereby allowing said articles to becomeproperly finished.

2. The method of claim 1 wherein said vibrating machine includes aprocess tub and an upright center post, and wherein said cushion of airbubbles is established primarily around said center post.

3. The method of claim -1 wherein said cushion of air bubbles isestablished by introducing into said vibrating machine a detergentcompound and a limited quantity of liquid just sutficient to create arelatively thick cushion of air bubbles.

4. The method of claim 3 wherein said abrasive materials are ofdifferent dimensions.

References Cited UNITED STATES PATENTS 2,548,264 4/1951 Howe 51316 X3,161,997 12/1964 Balz 51-316 LESTER M. SWINGLE, Primary Examiner

